1. Field of the Invention
The present invention relates to rigid, microcellular organic foams. The foam is made from naturally occurring biological or organic material and is formed by gelling a solution or, more commonly, an emulsion. The gel is frozen and freeze-dried to form a microcellular foam. The foam can be produced with any desired density from about 1 mg/cm.sup.3 to about 500 mg/cm.sup.3.
2. Description of Related Art
A myriad of applications exist for strong, low-density, inexpensive materials to manufacture lightweight articles. Synthetic polymers and foams, such as polystyrene, polyurethane, and Styrofoam.RTM., are commonly-used materials for these purposes. A soluble, lightweight material made from corn and wheat is also currently available. A continual demand exists for the development of ever lighter, stronger, cost-effective materials that are biodegradable and made from renewable resources.
The scientific research communities in government and academia would also like to produce very lightweight microcellular foams exhibiting a variety of characteristics. Researchers working with materials such as TPX (synthetic methylpentene polymer) and polystyrene have been unable to reach the very low densities and create the cell structures desired. The present invention addresses these diverse needs and is a biofoam produced from organic materials derived from biological organisms, such as algae.
Biofoam should not be confused with a different class of ultra-low density materials, namely aerogels, that were developed by another group at Lawrence Livermore National Laboratory. Aerogel is a true gel in which the gel structure must be maintained throughout the production process. In contrast, while the biofoam production process involves a gel stage, the end product is not a gel, but rather is an open-cell rigid foam material much like polystyrene. The different microscopic structures of the two materials leads to variances in their physical and chemical properties.
For example, the most common aerogel is a silica-based material that will not burn easily. Biofoam is an organic-based material that will burn without producing toxic fumes. The average cell or pore size of aerogel is about 100 times smaller than that of biofoam; aerogel pore diameters are about 0.02-0.03 microns, whereas biofoam cells have diameters of about 2-3 microns. The smaller pore size of aerogels makes them visibly transparent and better thermal and acoustic insulators than the visibly opaque biofoam. The major advantage of biofoam over aerogel is its lower production cost. Aerogel's complex production process involving supercritical extraction of solvents is time-consuming and expensive as compared to the freeze-drying procedure used in biofoam production. Furthermore, biofoam is a more robust material than aerogel that can withstand greater forces without fracturing or deforming. Biofoam can therefore be readily machined into different shapes.